Draper platforms are elongate harvesting heads that are mounted on the front of agricultural harvesters. They typically include an elongate rigid frame with two guide wheels, one guide wheel located on either side of the frame. Draper platforms are supported on a feederhouse which extends forward from the front end of the agricultural harvester. Draper platforms are also supported on the guide wheels using springs. The springs are typically mechanical (such as leaf springs or coil springs) or hydraulic springs (i.e. hydraulic cylinders coupled to gas-charged accumulators).
In one prior art design, hydraulic springs included hydraulic cylinders coupled to a single gas-charged accumulator commonly coupled to all of the hydraulic cylinders, including cylinders the spring mount the frame to the guide wheels and to the feederhouse of the agricultural harvester.
The advantage of this arrangement is that by charging or discharging fluid from the single gas-charged accumulator, the forces applied by all the hydraulic springs could be simultaneously increased or decreased, proportionately and while the agricultural harvester was underway, traveling through the field harvesting crops.
By simultaneously extending all the springs, the draper platform is raised higher above the ground, yet does not changing its side-to-side orientation. This is useful when the draper platform travels over rough terrain to prevent injury to the draper platform by increasing its ground clearance.
One problem with this arrangement was that the entire draper platform tended to tilt to one side or the other. This was due to the cylinders being coupled to a common gas-charged accumulator. Rather than holding the draper platform at the same height above the ground across the entire width of the draper platform, the four hydraulic cylinders coupled in parallel to a single accumulator permitted hydraulic fluid to flow back and forth between the hydraulic cylinders when the center of gravity of the draper platform shifted to the left or to the right. This fluid flow tended to empty cylinders on the heavier side of the draper platform and fill the cylinders on the lighter side of the draper platform. As a result, one end of the draper platform could sink and perhaps dig into the ground while the other end of the draper platform could lift upward into the air.
What is needed, therefore, is a draper platform suspension using hydraulic springs that solved the problem of draper platform tilting due to hydraulic fluid flowing back and for the from side to side. A solution to this problem is described in claim 1 herein. The other claims describe other features of the machine that provide additional benefits.